This invention relates to electronic digital processor systems, and more particularly to an organization of an MOS/LSI semiconductor chip adapted for performing the functions of a calculator.
Miniature electronic calculators were made possible by the integrated semiconductor arrays such as shown in U.S. Pat No. 3,891,921, issued June 25, 1974 to Kilby, Merryman & VanTassel, assigned to Texas Instruments. In the ten years since the invention of integrated arrays for calculators, many advances in technology have resulted in great improvements in size, power, cost, functions and reliability in miniature calculators. All of the primary electronic functions of a calculator were incorporated into a single low cost MOS/LSI chip as described in patent application Ser. No. 163,565, (now Ser. No. 420,999) filed July 19, 1971 by Gary W. Borne and Michael J. Cochran, assigned to Texas Instruments; this "one-chip" calculator resulted in a versatile, 8 or 10 digit, full floating point calculator which eventually sold for less than $40. Further developments such as set forth in U.S. Pat. No. 3,892,957 issued July 1, 1975 to John D. Bryant, and U.S. Pat. No. 3,934,233 issued Jan. 20, 1976 to Roger J. Fisher and Gerald D. Rogers, both assigned to Texas Instruments, allowed more of the circuitry such as segment drivers, clock generators and the like to be included on the MOS/LSI chip, and very low power operation was achieved. This resulted in 5-function calculators which sold for less than $20 and could use low cost, throw away batteries with reasonable battery life. High level scientific calculators with log and trig functions, exponentiation and other complex functions, were made possible at low cost by an MOS/LSI chip set which is described in U.S. Pat. NO. 3,900,722, issued Aug. 19, 1975, to Michael J. Cochran and Charles P. Grant; calculators of this type now sell at less than $50 compared to several hundred dollars only two years ago. A general purpose digit processor capable of providing many different calculator functions as well as being a microcomputer with self-contained ROM, RAM, and clock oscillator is the subject of U.S. Pat. No. 3,991,305, issued Nov. 9, 1976, filed Nov. 19, 1974 by Joseph H. Raymond and Edward R. Caudel, assigned to Texas Instruments. A major innovation in reducing the cost is that set forth in U.S. Pat. Nos. 4,014,012 and 4,014,013, issued Mar. 22, 1977, filed Apr. 7, 1975 by David J. McElroy and by Edward R. Caudel; this consisted of eliminating digit driver devices so that no semiconductor components or devices were needed outside the MOS/LSI, except of course the keyboard, display, battery and ON-OFF switch. The ON-OFF switch was incorporated into the keyboard as a momentary push-button device as set forth in copending application Ser. No. 695,886 filed June 14, 1976 by David J. McElroy, and Ser. No. 700,672 filed June 28, 1976 by McElroy, Graham S. Tubbs and Charles J. Southard, both assigned to Texas Instruments.
All of these development efforts have aimed at reducing the manufacturing cost of the calculator and increasing its functions. These are the objectives of the present invention.
While simple addition, subtraction, multiplication and division can be executed so rapidly on a calculator of the types mentioned above, the execution time becomes a potentially annoying factor where complex functions such as logs and trigs are introduced. Indeed, the execution time in some cases becomes the limiting factor which prevents math functions from being added to a new calculator design.
It is a principal object of the invention to provide an MOS/LSI calculator chip which has reduced execution time for mathematical operations. Another object is to provide a digit processor system having an improved instruction set. A further object is to provide a versatile and low cost calculator or digital processor device.